Unwanted transforms in animation
You use Replace blending mode for these strips, but I would say you probably used Add when you edited action. Changing back to "Add" blend type - seems solved the issue here.



There of course matter what blend mode you used while editing, also there matters what action is used bellow.





BTW

To do changes on imported animations I would use NLA editor to adjust animation. If you use GGT add-on its automatically imported as NLA action strips (animations).

I cleaned up all unused tracks and left only one to keep it more clear.
("Riffle_Crouch_Walk")




Action editor
- create a new action
(or delete existing and add keyframe for selected bones in Pose mode)
- here you can do all edits that are Replaced, Added or what ever (is set in NLA strip properties) on top of imported track (action)

NLA editor
- top action is always used (if not disabled)
- top row (with dope sheet icon) is always editable one
- all bellow (with star icon) are "Push Down" for strip mixing
(like now "Riffle_Crouch_Walk" imported action)

When you finish edits, you can search "Bake Action" (with cursor inside NLA editor) into one animation.

See blend file